Hydril-type connector

ABSTRACT

An improved pressure type connection on stepped-thread Hydril-type tubing and casing tool joints is disclosed, wherein a secondary sealing means is included between the stepped threaded areas of the Hydril-type connector. The secondary sealing means includes an annular ring of relatively rigid, internally tenacious plastic or rubber material, which serves to contain well pressure if the metal-to-metal sealing surfaces on the pin and box members of the Hydril-type connector are damaged. With such secondary sealing rings, damaged Hydril-type connectors can still be used, without having to scrap same, or having to repair the damaged area at great expense.

This is a divisional application of Ser. No. 871,336, filed Jan. 23,1978 now U.S. Pat. No. 4,496,175, which is a division of Ser. No.736,492, filed Oct. 28, 1976, now U.S. Pat. No. 4,085,951.

BACKGROUND OF THE INVENTION

In oil fields, drill strings are frequently connected by Hydril-typeconnectors, which involve a two step thread design, as is well known tothose in the art. For instance, Hydril-type connectors are disclosed inU.S. Pat. No. 2,532,632, the disclosure of which is hereby incorporatedby reference for the teachings of the Hydril-type connectors therein.

The prior art has made extensive use of "O" rings and similar sealingmeans, in the sealing of pipes and the like. See, for instance, U.S.Pat. Nos. 3,054,628; 3,167,333; 2,980,451; 2,889,733; 2,813,567;2,770,477; and 2,553,340. Generally the sealing rings or gaskets ofthese prior art patents have been made of Teflon or similar plasticmaterial.

The use of rings of plastic or rubber, or the like, in rotary tools isalso known to the art, see, for instance, U.S. Pat. Nos. 2,102,072 and2,110,127. Finally, the use of Teflon as a sealing ring in Hydril-typeconnectors is disclosed in U.S. Pat. Nos. 2,907,589 and 3,100,656. Inthese patents, the Teflon seal ring is located in the area of the freeterminal forward end of the pin member of the Hydril-type connector. Ifsuch sealing rings are located on the pin member, they are highlysusceptible to damage, and if located on the box member they are quitedifficult to install, and subject to a tendency to be locally derangedin an unpredictable manner as the joint is made up.

The present invention generally relates to improvements in threaded-typejoints and methods of making same, and in particular relates to thedesign and construction of sealed, screw-threaded oil well tubing anddrill string joints which are capable of being rapidly made up topostive pressure seal condition, and rapidly broken apart without damageto the threads or seal during either make up or breaking of the jointunder conditions of repeated severe usage in the field. In particular,the present invention is directed to improvements in Hydril-typeconnectors, wherein the connector is capable of maintaining full wellpressure, even though the conventional metal-to-metal seating surfacesof the Hydril-type connector are damaged. The present invention isapplicable to inserted joints, wherein one pipe end is screwed directlyinto the end of another pipe end, to couplings in which the opposed endsof two pipes are threaded into a tubular collar, and to other similartypes of pipe end connections.

As acknowledged hereinabove, many different designs of screw threadedpin and box type tubing and drill pipe joints have been proposed by theprior art. However, in spite of the many proposals, a number of problemshave remained unsolved, especially those problems having to do with amethod of adequately and enduringly sealing a Hydril-type connectorafter the metal-to-metal seating surfaces have been damaged, which is afrequent occurrence, against the extremely high fluid pressures whichare encountered in deep drilled oil and gas wells. For instance, suchpressures might range as high as 15,000 psi.

The rubber O-rings and compressible rubber gaskets, such as those of thepatents acknowleged hereinabove, have from time to time been used toseal pipe and tubing joints, and under certain operating conditions,especially when relatively low pressures are involved, they have provento be thoroughly satisfactory. However, such seals have not beensuitable for use under the high temperature and pressure conditionswhich are encountered in deep oil and gas wells. For one thing, theserelatively thin rubber rings when used in the prior art joints tend tobe badly damaged, and often rendered useless, by being extruded underthe well pressure into small clearances between the joint members at theseal ring groove. Compressive ring gaskets, such as of rubber andasbestos, have also been found to be susceptible to damage, probably asa result of a combination of sliding friction and high compressiveloads, during make up of the pipe joint with power tools.

Joints used for the purpose of connecting drill pipe lengths or tubinglengths must be made up with a tight fit on tapered lateral contactsurfaces in order to provide the required degree of rigidity needed toresist lateral bending stress with a minimum of fatigue. It is, however,difficult to produce sealed joints having both a tight fit on tapered,lateral contact surfaces, and a longitudinally compressed ring gasket,as even very small variations in the machining of the tapered lateralcontact surfaces results in significant displacement variations in thelongitudinal make up of the joints, with resultant differences of degreein the amount of compression applied to the ring gasket, which willsometimes be damaged by too great a compression, or may be compressedinsufficiently to adequately seal the joint.

Difficulties of this nature have lead to the use of special pipe andtubing joints which have tapered seating elements employing highlypolished metal-to-metal fits as a means of sealing against very high oilpressure, and such joints, when made up carefully under idealconditions, are entirely capable of sealing against such high wellpressures. This type of joint, referred to hereinafter as theHydril-type connector, is generally more costly to manufacture than moreconventional pipe and tubing joints, and the polished sealing surfacesor seats are quite susceptible to damage when the joints are made up andbroken out under operating conditions encountered in the oil fields.Damage may occur as a result of direct or sliding impact of the pin seatagainst the end of the box when the lower end of a suspended, relativelyheavy pipe stand is stabbed into a joint on the upper end of the pipewhich precedes the suspended pipe stand into the well.

Furthermore, the polished metal-to-metal sealing areas or seats are alsoquite susceptible to damage at the time the joints are screwed together,as even quite small particles of dirt or sand, if trapped between themating seats, are capable of scoring or producing galling which maycompletely destroy the effectiveness of the metal-to-metal seal.Excessive friction, caused by overtightening, lack of lubrication, orrapid make up, will occasionally cause the tight fitting metal-to-metalseats to gall during the last fraction of a turn as the joints arescrewed together.

In an effort to avoid the entrapment of dirt and sand particles betweenthe seating surfaces as the joints are screwed together, the prior arthas customarily made the metal-to-metal contact area between the seatsrelatively narrow. The prior art may provide one joint member with anarcuate seating surface and the mating member with a conical seatingsurface to obtain a line of contact between the two surfaces. However,such narrow seating surfaces are not generally desirable because theyare quite vunerable to attack by the corrosive fluids which are oftenpresent in oil and gas wells. In this regard, the corrosive needpenetrate only a relatively short distance in order to completelydestroy the line of metal-to-metal contact existing between the twojoint surfaces, and thereby destroy the seal.

Thread damage is frequently caused by the vertical stabbing of threadedpin ends of suspended heavy pipe stands into threaded box ends of pipeor pipe collars supported beneath the pipe stands. This damage usuallyoccurs when the entire stabbling load falls on the relatively thin andfrail thread ends of the threaded pin and box members. A damaged endthread on one joint member will often damage, and occasionally destroy,a number of additional threads on both members should the pin and box bescrewed together before the thread end damage is discovered.

The Hydril-type connectors, because of their relatively delicate sealingareas, are easily damaged. Damage to the Hydril-type connector sealingareas has heretofore required that the unit be scraped, or shop repairedat great expense.

The Hydril Company commercially offers a patented tubing connection,with a Teflon ring located in the box member at a location such thatwhen the connection is made up the ring will be at the free terminal endof the pin. It is indicated that the prime purpose of this ring is tocomplete the corrosion protection afforded by plastic coated pipe. Theadvertising material also indicates that the connection may be specifiedwhere an additional highpressure seal is desired.

The Rucker Atlas Bradford Company has offered leak-proof tubing to thetrade, using conventional thread profile, but modifying the coupling bymachining out one and one-half threads near each end of the internallythreaded coupling and installing a Teflon ring in the resultantretaining groups. In another version, a pin and box member design isprovided wherein a groove is machined inside the box member to retain aTeflon seal ring.

SUMMARY OF THE INVENTION

The present invention is directed to a joint for interconnecting a pairof pipes, preferably pipes used in an oil field drill string. A jointincludes coaxial pin and box members which have interengaged externaland internal two step threads respectively. The threads havesubstantially the same pitch and outline characteristics, and upon thepin member being screwed about the its longitudinal axis forwardly intothe box member, the pipes are held against separation. The annularshoulder member on the pin member between the two threaded areasincludes an annular recess opening radially outwardly and extendingabout the shoulder area, with an annular continuous ring of Teflon orthe like received in the recess and being compressed between the pinmember and the box member to seal the pipe even if the primarymetal-to-metal seating surfaces of the joint are damaged.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be more readily understood by reference tothe accompanying drawings wherein:

FIG. 1 is a cross-sectional view of a typical joint of the presentinvention;

FIGS. 2 and 3 are expanded views of the free terminal forward end of thebox and the pin, respectively, of FIG. 1;

FIG. 4 is an enlarged view of the pin member of FIG. 1;

FIG. 5 is a side view of the sealing ring used in the present invention;

FIG. 6 is a cross-sectional view of the ring of FIG. 5, taken along theline 6--6;

FIG. 7 is a view similar to FIG. 6, but illustrating a differentembodiment of the sealing ring member;

FIG. 8 is a view similar to FIG. 6, illustrating yet another embodimentof the sealing ring; and

FIG. 9 is an expanded view of the sealing ring 24 of FIG. 1.

In FIGS. 1, 2, 3 and 4, the joint 1 shown therein includes pin member 2and box member 3 having interengaged two step threads, with threads 4and 5 interengaged in one step, and threads 6 and 7 interengaged in asecond step. The pin and box member are of the two-step type, with pinthreads 4 and 6 cut on steps 8 and 9 respectively and being of the samepitch and outline characteristics. In the similar manner, box memberthreads 5 and 7 are complimentary to pin threads 4 and 6 and are cut onsteps 10 and 11. At the outer end of the box there is provided a taperedbox stop shoulder 12 which is complimentary to an opposed pin stopshoulder 13, while at the inner end of the box there is a square cutshoulder 14 and a complimentary square cut pin shoulder 15. When thejoint 1 is fully made-up, tapered pin and box stop shoulders 20 and 21are in compressive engagement near the forward end of the pin.

The box and pin members have rather shallow bevels or chamfers 18 and 19intersecting the box and pin bores 16 and 17 and also intersecting thebox shoulder 14 and the pin foremost extent 15, respectively. The bevelsare generally coaxial and typically will extend at around 20 degreesangularity with the bores 16 and 17 as illustrated.

The mating shoulders provide metal-to-metal seating surfaces, serving toseal the joint against outward escape of high fluid pressure from thejoint. However, upon damage of one or more of the shoulders, the jointmay no longer be capable of retaining full well pressure. The presentinvention is directed to providing a connector which will contain fullwell pressure in the pipe, even though the mating metal-to-metalshoulders are damaged.

To provide this secondary sealing means, which seals the interior of thepipe against the fluid pressure therein, in the shoulder area 22 betweensteps 8 and 9 of the pin a groove 23 is provided. This groove istypically of a width corresponding to about 1 to 5 threads, typicallyabout 11/2 to 2 threads in width. An annular ring 24 of relatively rigidinternally tenacious plastic or rubber material, such as, for instance,of Teflon (polytetrafluoroethylene) is provided in the groove. The ring24 is of such a size that upon full make up of the joint, the ring isplaced under compression between shoulder 26 on pin member 2 andshoulder 27 on box member 3. Generally the ring will be compressedbetween 10% and 50% of its original width. The ring can take variousshapes, and the preferred shape is shown in FIGS. 5 and 6, wherein ring50 includes an annular ring 51 of square cross-section, having moldedsegments 52 integral therewith on the inner side of the ring. Thesegments permit the ring to be slipped over the threads of the pin andretained in groove 23. As will be more clearly seen in FIG. 4, groove 23is defined by side walls, an interior surface and an opening oppositethe interior surface. The side walls at the opening extend in adirection which is generally perpendicular to the axis of the pin andbox members. The opening to groove 23 is radially removed from theinterior surface of the groove.

The ring 70 of FIG. 7 is an alternative construction, wherein an annularring 71 of square cross-section includes on its inner surface arelatively thin ring 72, having a plurality of slits (not shown)therein, with slit ring 72 permitting the ring to be slipped over thethreads and retained in the groove of the pin member 2.

Finally, FIG. 8 illustrates yet another embodiment of the sealing ring,wherein ring 80 is of square cross-sectional area. This ring may beinstalled by heating the ring so that the ring expands enough to permitit to be slipped over the pin member threads into groove 23. It is alsopossible that ring 80 could be actually molded in place in groove 23.

In FIG. 9, ring 24 is illustrated in a compressed comdition. Uponmake-up of the joint, ring 24 located in groove 23 is compressed betweenshoulder 25 of box member 3 and shoulder 26 of pin member 2.

A number of other materials can be used in the construction of thesealing ring 24 in addition to Teflon, including such diverse materialsas Mylar, hard rubber, nylon, delrin, and the like. Importantconsiderations in the selection of a sealing ring material is that thematerial be compressible, relatively rigid, and internally tenacious.With Teflon rings, for instance, it is believed that rings designedalong the lines described hereinabove will seal Hydril-type connectorsup to the bursting strength of conventional oil field pipe itself.

It will be appreciated by those in the art that a considerable costsavings can be achieved with the use of the present invention, becauseof the high dollar volume of the wasted drill strings wherein theHydril-type connector threads or seating surfaces are damaged. A typicalunit of pipe having Hydril-type connectors thereon would have a lengthof about 30 feet, and would cost about $6.75 per foot. Thus, a typicalunit would cost about $200.00 and thousands of such units are discardedannually by the oil and gas drilling industry.

It will be readily appreciated that the sealing ring 24 of the presentinvention can be installed on new, unused Hydril-type connectors.However, it is believed that the cost involved on putting such rings onnew connectors probably would not justify that approach, and thus it ismost likely that the present invention will only be used on damagedHydril-type connectors. Thus, upon the initial make up of the repairedHydril-type connector, using the sealing ring of the present invention,the sealing ring would be expected to withstand full well pressure.

Ring 24 should have a outer diameter such that it does not interfer withthe threads 5 passing thereby. The use of segments 52 or the likepermits some measure of inner movement of ring 51, but it is normallypreferred that the outer diameter of ring 51 be less than the innerdiameter of box threads 5.

What is claimed is:
 1. A method of repairing a damaged joint forinterconnecting a pair of oil well pipes, said joint comprising coaxialmale and female members respectively including interengageable externaland internal first threads, and interengageable external and internalsecond threads, said first threads on said male member being adjacentthe free terminal forward end of said male member and being of smallerouter diameter than said second threads, said threads when interengagedcapable of holding said pipes against separation, said first threads andsaid second threads having substantially the same pitch and outlinecharacteristics, said male member being screwable about said axislongitudinally forwardly into said female member, at least one pair ofmetal-to-metal seating surfaces on said male and female members, whereina seating surface is located at or adjacent the free terminal forwardend of said female member, said at least one pair of seating surfacesbeing sealingly interengageable when undamaged, at least one seatingsurface being damaged so as to no longer be capable of maintaining apressure differential thereacross, and an annular shoulder area on saidmale member between said first threads and said second threads, saidmethod comprising forming an annular recess in said shoulder area, saidrecess being a groove having side walls, an interior surface and anopening, said side walls extending in a generally radial direction fromsaid interior surface to said opening, said groove being enterable froma radial direction of the joint and opening radially outwardly andextending about said shoulder area, and providing in said annular recessan annularly continuous ring of plastic or rubber material, andextending about the periphery of said interior surface, said ring beingcompressible by and between said pin member and said box member to forma high pressure seal to seal the interior of said pipe from the exteriorof said pipe.
 2. A method as claimed in claim 1, wherein said ring is ofa plastic material.
 3. A method as claimed in claim 1, wherein saidplastic material is polytetrafluoroethylene.
 4. A method as claimed inclaim 1, wherein said metal-to-metal seating surfaces comprise taperedstop shoulders.
 5. A method as claimed in claim 1, wherein a stopshoulder is located at or adjacent the free terminal forward end of saidmale member and a second stop shoulder is located at or adjacent thefree terminal forward end of said female member.
 6. A method as claimedin claim 1, wherein the length of said first and second threads isbetween about one third and about five times the internal diameter ofsaid pipes.
 7. A method of providing a secondary seal in a joint forinterconnecting a pair of pipes, said joint including a primarymetal-to-metal seal and coaxial pin and box members respectivelyincluding interengageable external and internal first threads andinterengageable external and internal second threads, said first threadson said pin member being adjacent the free terminal forward end of saidpin member and being of smaller outer diameter than the said secondthreads, said threads when interengaged holding the pipe againstseparation, said first threads and said second threads havingsubstantially the same pitch and outline characteristics, said pinmember being screwable about its axis longitudinally forward into saidbox member, metal-to-metal seating surfaces on said pin and box membersforming said metal-to-metal seal when undamaged and in interengagement,an annular pin member shoulder area including a stepped portion on saidpin member between said first threads and said second threads, anannular box member shoulder area including a stepped portion on said boxmember between said first threads and said second threads, said methodcomprising forming an annular recess in said shoulder area, said recessbeing an annular groove defined by side walls, an interior surface andan opening opposite the interior surface, said side walls extending atsaid opening in a direction generally perpendicular to the axis of thepin and box members, and providing in said annular recess an annularlycontinuous ring of plastic or rubber material, said ring beingcompressible by and between said pin member and said box member to formthe secondary seal which can function as the primary high pressure sealto seal the interior of the pipe from the exterior of the pipe shouldthe primary metal-to-metal seal be damaged.
 8. A method as claimed inclaim 7, wherein said ring is of a plastic material.
 9. A method asclaimed in claim 7, wherein said plastic material ispolytetrafluoroethylene.
 10. A method as claimed in claim 7, whereinsaid metal-to-metal seating surfaces comprise tapered stop shoulders.11. A method as claimed in claim 7, wherein a stop shoulder is locatedat or adjacent the free terminal forward end of said pin member and asecond stop shoulder is located at or adjacent the free terminal forwardend of said box member.
 12. A method of providing a secondary seal in anoil field pipe joint, said joint having at least one primarymetal-to-metal seal, said joint comprising coaxial tubular male andfemale members respectively including interengageable external andinternal first threads, and interengageable external and internal secondthreads, said first threads on said male member being adjacent the freeterminal forward end of said male member and being of smaller outerdiameter than said second threads, said threads holding the joint whenmade up against separation, said first threads and said second threadshaving substantially the same pitch and outline characteristics, saidmale member being screwable about its axis longitudinally forwardly intosaid female member, metal-to-metal sealing surfaces on said male andfemale members, said surfaces being interengageable when undamaged, anannular male member shoulder providing a stepped portion on said malemember between said first threads and said second threads, an annularfemale member shoulder providing a stepped portion on said female memberbeing said first threads and said second threads, said method comprisingproviding receiving means for receiving a sealing ring in a shoulderarea, said receiving means being an annular groove defined by sidewalls, an interior surface and an opening opposite said interiorsurface, said side walls extending at said opening in a directiongenerally perpendicular to said axis, and providing an annularlycontinuous ring of plastic or rubber material in said receiving means,said ring being compressible by and between said male member and saidfemale member when said joint is made up to seal the interior of thejoint from the exterior of the joint if the primary metal-to-metal sealis damaged.
 13. A method of providing a secondary seal in a joint foroil field pipe, said joint having at least one primary metal-to-metalseal, said joint comprising coaxial tubular male and female membersrespectively including interengageable external and internal firstthreads, and interengageable external and internal second threads, saidfirst threads on said male member being adjacent the free terminalforward end of said male member and being of smaller outer diameter thansaid second threads, said threads holding the joint against separationwhen said joint is made up, said first threads and said second threadshaving substantially the same pitch and outline characteristics, saidmale member being screwable about its axis longitudinally forwardly intosaid female member, metal-to-metal sealing surfaces on said male andfemale members, said surfaces being interengageable when undamaged, anannular male member shoulder providing a stepped portion on said malemember between said first threads and said second threads, an annularfemale member shoulder providing a stepped portion on said female memberbetween said first threads and said second threads, said methodcomprising providing receiving means for receiving a sealing ring in ashoulder area, said receiving means being located between the membershoulder of said shoulder area and the first threads of that member, andbeing an annular groove in said shoulder area, said groove having sides,an interior surface and an opening which is radially removed from saidinterior surface, said receiving means being an annular recess openingin a radial direction from and extending about said shoulder area, andproviding an annularly continuous ring of plastic or rubber material inand extending around the periphery of said receiving means, said ringbeing compressible by and between said male member and said femalemember when said joint is made up to seal the interior of the joint fromthe exterior of the joint if the primary metal-to-metal seal is damaged.14. Method of claim 13, wherein said receiving means is providedproximate one of said shoulders.
 15. Method of claim 13, wherein saidreceiving means is provided contiguous to one of said shoulders. 16.Method of claim 13, wherein said receiving means is contiguous to saidmale member shoulder, and proximate the first threads of said malemember.
 17. Method of claim 13, wherein said receiving means is providedproximate one of said shoulders.
 18. Method of claim 13, wherein saidreceiving means is provided contiguous to one of said shoulders. 19.Method of claim 18, wherein said receiving means is contiguous to saidmale member shoulder and proximate the first threads of said malemember.